While Emma Watson denied rumors of starring in the erotic “Fifty Shades of Grey,” she didn’t hesitate to strip down for Earth Day.

The 22-year-old, no longer the little girl known as Hermione Granger in the Harry Potter series, posed nude for James Houston’s Natural Beauty book to benefit Green Global USA, a non-profit dedicated to fighting global warming. The steamy photos showed a soaked Watson accessorizing with orchids.

Turning to Twitter, Watson announced the news to her fans, typing, “My friend is supporting GlobalGreenUSA with his book Natural Beauty. It's out now. : ) X.”

Surprising for a girl who denounced the “Fifty Shades of Grey” film, also tweeting, “Who here actually thinks I would do 50 Shades of Grey as a movie? Like really. For real. In real life.”

Watson’s “friend,” the New York-based photographer and activist James Houston, explained his inspiration: "This project merges my longtime interest in the human form and my passion for the natural world," He continued to say, "I hope to raise environmental awareness among the younger audience through this project."

The 120-page book, featuring other naked celebrities and models (particularly women), debuts during World Earth Week 2013 at the MLK Gallery in New York at the end of April. A 12-week web series premiering March 25 on “The Making of the Natural Beauty Campaign” also promotes the initiative, by featuring interviews and behind-the-scenes footage.

President and CEO of Global Green USA, Matt Petersen expressed enthusiasm at the idea: “I was honored when James [Houston] came to Global Green asking if we would be his charitable partner and beneficiary on Natural Beauty.” He concluded, “When an individual like James goes to great lengths to take responsibility and action, it helps inspire others to join the fight against environmental degradation and climate change.”

He failed to mention the degradation of young women in the process. But hey, sex sells, right?